1. Field of the Invention
This invention relates to a wood planing machine, more particularly to a wood planing machine with a tightening unit for preventing loosening of a cutter carriage thereof during a planing operation.
2. Description of the Related Art
FIGS. 1 and 2 illustrate a conventional wood planing machine 10 disclosed in U.S. Pat. No. 5,771,949. The wood planing machine 10 includes a base 11 with two pairs of upstanding posts 12 disposed at the corners of the base 11 for supporting a cutter carriage 13 thereon, a height adjusting unit for adjusting height of the cutter carriage 13 relative to the base 11 via a handle 16 which is mounted on a top end of the wood planing machine 10, and a carriage locking mechanism 20 for positioning the cutter carriage 13 on the posts 12. The cutter carriage 13 cooperates with the base 11 to confine a wood passageway therebetween for passage of a workpiece 17, and includes a pair of opposite threaded castings. The height adjusting unit includes a pair of screw rods 14 extending upright from and disposed at two opposite sides of the base 11 between the posts 12 for rotating about axes defined by the screw rods 14, and an assembly of sprockets and a chain connected to the screw rods 14. The screw rods 14 threadedly engage the castings of the cutter carriage 13 so as to move the cutter carriage 13 upwardly and downwardly along the posts 12. The locking mechanism 20 is operable for providing a clamping force to hold the cutter carriage 13 on the posts 12 after the cutter carriage 13 is moved to a desired position by operation of the screw rods 14.
The wood planing machine 10 is disadvantageous in that since there are clearances between engaged teeth of the screw rods 14 and the castings of the cutter carriage 13, vibration of the cutter carriage 13 and clashing between the castings of the cutter carriage 13 and the screw rods 14 tend to occur during operation of the wood planing machine 10. Moreover, the vibration of the cutter carriage 13 has an adverse affect on the precision of the planed workpiece.
Therefore, it is an object of the present invention to provide a wood planing machine with a tightening unit that is capable of overcoming the drawbacks described above.
Accordingly, a wood planing machine of this invention comprises: a generally rectangular base having four corners; four parallel hollow posts that extend upright from the four corners of the base, respectively, and that are formed with elongated slots extending along lengths of the posts, respectively; four screw rods respectively disposed in the posts, and rotatable about axes defined by the screw rods, each of the screw rods including an engaging portion accessible via the slot in the respective one of the posts, the engaging portion having upper and lower helical surfaces; four sprockets disposed underneath the base and connected respectively to bottom ends of the screw rods; a chain engaging the sprockets so as to synchronize rotations of the screw rods; a cutter carriage including a pair of parallel carriage seats, each of which is transverse to and is mounted movably on two adjacent ones of the posts, and each of which includes top and bottom plates and two opposite side plates that interconnect the top and bottom plates and that are respectively formed with openings confronting the slots in the respective ones of the posts; four threaded members mounted respectively on the side plates of the carriage seats, each of the threaded members including a bracket plate mounted adjustably on a respective one of the side plates, and a sector-shaped threaded portion projecting from the bracket plate through the opening in the respective one of the side plates to threadedly engage the engaging portion of a respective one of the screw rods so as to permit the carriage seats to be moved simultaneously along the posts when the screw rods rotate synchronously, the bracket plate of each of the threaded members being formed with an engaging hole defined by a hole-confining wall, the threaded portion of each of the threaded members having upper and lower helical surfaces, the hole-confining wall of the bracket plate of each of the threaded members having top and bottom wall portions; and a tightening unit including four eccentric members that are mounted rotatably and respectively on the bracket plates of the threaded members, each of the eccentric members including a rotatable shaft and an eccentric wheel that extends radially from and that is eccentric relative to the rotatable shaft, that is inserted in and that constantly and rotatably engages the top and bottom wall portions of the hole-confining wall of the bracket plate of a respective one of the threaded members, and that is rotatable together with the rotatable shaft between a first engaging position, in which, the eccentric wheel moves the respective one of the threaded members upwardly relative to a respective one of the screw rods so as to permit engagement between the upper helical surface of the threaded portion of the respective one of the threaded members and the lower helical surface of the engaging portion of the respective one of the screw rods, and a second engaging position, in which, the eccentric wheel moves the respective one of the threaded members downwardly relative to the respective one of the screw rods so as to permit engagement between the lower helical surface of the threaded portion of the respective one of the threaded members and the upper helical surface of the engaging portion of the respective one of the screw rods.